in the last few years china has been producing some crazy stuff.
Some of them can compair to a very high end guns, because litterally there knocking off everything about a high end guns.
Some china aeg's come with clones upgrades that are simply a stolen designs, Like king arms highspeed gear sets in Certin A&K guns,
(of course they dont say King arms on them, but they look identical to the KA gear sets because someone bought a set and casted a mold of them)
really all the china guns need is someone that pays attention to doing shim jobs and all of that correctly to go in there and put it together taking there time.
and by just heat treating the china gears there actually really nice gears some of them last forever